CONDITION OF THERMAL EXPANSION INSIDE CAVITY AND DETAILS OF TROUBLE
For the floating type/soft seat ball valve, and liquid fluid:
- In case of temperature of fluid and atmosphere has some increasing(for example ”water: 30°C”, depends on fluid), and valve not operated for the time of increasing temperature.
- In case of valve position is “Full Open” for the time of increasing temperature,
- In case of valve position is ”Full Close” for the time of increasing temperature and differential pressure between upstream and downstream is below 98MPa.
- In case of operation frequency is little and ball seat is
The above conditions are happened more than 2 subjects, fluid inside body cavity(inside pocket) is increased pressure by thermal expansion. This condition is called “Thermal Expansion Inside Cavity”.
THERMAL EXPANSION INSIDE CAVITY CAN CAUSE OTHER PROBLEMS SUCH AS:
- Operation torque is increased suddenly, and happened operation problem for on-off valve and manual
- There is possibility to get damage for seal
- There is a possibility to get damage for valve (especially for cast iron body.)
PREVENTIVE MEASURES FOR THERMAL EXPANSION
- Making a hole (bypass) body cavity to valve port. (For the time of increasing temperature and valve position “Full Open”, body cavity and port is same pressure condition.) Standard Spec. for HF5 model.
- In case of increased temperature, valve position “full open” and fluid pressurizing direction 1-way, make a relief groove on ball seat at upstream side, make a hole on ball face at upstream side pass to port.
- In case of increasing temperature, valve position “full close” and fluid pressurizing direction non-fixed, valve should be used Trunnion type ball valve.
PRESSURE RELIEF HOLES IN BALL VALVES
Pressure relief vents in ball valves serve to prevent the damaging pressure build up which is inherent in certain valve applications. Two type of vents are available in Bonomi ball valves: the “A” type with connects the ball slot with the port, and the “B” or upstream type face of the ball. Heating of liquid media trapped within the valve body center chamber can cause the internal pressure to rise to levels which can permanently distort the seats. Damage is progressive: the cycle begins when the valve body, filled with liquid, is heated usually through conduction from hot flowing media. As the trapped media expands, it applies intense pressure to the outside rim of the seats forcing them inwardly toward the port.
Only a small amount of deformation is sufficient to drop the internal pressure and stop further deformation, but when applied, pressure is relieved the seats don’t quite regain their original shape.
Succeeding cycles admit fresh liquid to center chamber, filling the space now enlarged through seat distortion from preceding cycles. The process usually continues by stages until one of the seats collapses, the buckled section intruding into the port area. When the valve is operated after the seat buckles, the ball port may shear a piece from the inside diameter as the valve is operated leaving the seat with the appearance of having been bitten.
LOW TORQUE BACK SEAT DESIGN
Striving for low operating torque on ball valves has been the goal of every ball valve manufacturer since the product was invented. If we could turn off a ball valve with our pinky finger and still expect bubble tight sealing, under various pressures, we would all be jumping for joy, wouldn’t we? All Bonomi direct mount ball valves are designed with the lowest possible operating torque of all other commodity style ball valves used in the industry today. How is this possible?
The traditional “floating” style ball valve that is so widely used today is assembled by forcibly compressing the components together in order to make an effective ball to seat connection. This ensures tight sealing in the field, a major priority. However, during the assembly process the ball is “driven” to seal [squished might be a better term to use] on the downstream seat. Because of this assembly technique, the total contact of the O.D. of the ball to the downstream TFE seat forms a “set” or a deformation/indentation to the seat itself. This downstream sealing is the industry standard and perhaps the only way for all commodity ball valves to operate and properly seal. Unfortunately the end result is a very high initial breakaway torque due to the ball dislodging itself from the deformed downstream seating surface.
All Bonomi direct mount ball valves incorporate technologically advanced “O” ring-backed TFE seats and precision round balls that dramatically reduce operating torque. Viton™ “O” rings are inserted into a groove formed into the backside of the TFE seat as a unit prior to assembly. Once the valve is assembled and tested, the “O” rings exert only a minimum amount of pressure on the TFE seats, creating a seal on both the upstream and downstream side of the ball. This technique is similar to the dynamics of trunnion-style ball valves. Since the force exerted on the ball through the seats is uniform with the O.D. of the ball, the resulting friction between the ball and the seating surface is substantially reduced.
Furthermore, the stem sealing design of Bonomi direct mount valves also plays a role in lowering the torque. After each direct mount forging or investment casting is machined, they are transferred to a secondary “burnishing” operation performed on the stem sealing area. This special burnishing creates a micro finish in the I.D. area of the stem, and an ideal stem to casting fit. With the use of dual Viton™ “O” ring seals and two TFE auxiliary seals, the perfect ball valve stem seal results, never requiring stem adjustment, as is so common to conventional style ball valves, and reducing friction while lowering the torque even further.
The technological advancement of superior stem sealing and ”O” ring-backed seat designs allow Bonomi direct mount ball valves to enjoy the reputation of having the highest performance and lowest operating torque in the industry. Lower operating torque equates to the use of smaller size actuators, which in turn leads to a smaller profile and, of course, a less expensive package.
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